function L = Lpara(f)
global nx ny nz kz dzt1p5
% L = zeros(nx,ny);
L = -kz*kz*f;
% L(:,:,2:end-1) = (f(:,:,1:end-2)-2*f(:,:,2:end-1)+f(:,:,3:end))*dzt1p5;
% L(:,:,1) = L(:,:,end-1);
% L(:,:,end) = L(:,:,2);
end